The US state of Oklahoma executed a convicted murderer who made a reference to the "very close race" for the White House won by President Barack Obama in his final words, officials said.

The US state of Oklahoma on Tuesday executed a convicted murderer who made a reference to the "very close race" for the White House won by President Barack Obama in his final words, officials said.

Garry Thomas Allen, whose execution was stayed three times, was declared dead by lethal injection at 2310 GMT, just under an hour after polling stations closed in the state.

"Obama won two out of three counties," Allen said shortly before he was put to death, according to Jerry Massie, spokesman for the Oklahoma Department of Corrections told AFP. "It's going to be a very close race."

The 56-year-old appeared surprised the execution would take place, Massie said.

Allen was sentenced to death for the 1986 murder of the estranged 24-year-old mother of his two young children. He lost an eye in a scuffle with a police officer shortly afterwards.

His lawyers had argued that Allen, who was hospitalized with psychological problems and has had a history of alcoholism and drugs, could not be held accountable for his actions. The Supreme Court rejected his final appeal on Tuesday.

Allen is the fifth death row inmate to be executed in Oklahoma this year and the 36th in the United States as a whole, according to the Death Penalty Information Center.